Timed trunk release



May 23, 1950 T. ANDERSON ETAL 2,509,050

TIMED TRUNK RELEASE Filed Oct. 29, 1948 5 Sheets- Sheet l w S wh.

.rAA/DERso/v McoooARo @6. M

ATTORNEY' /N VEN TORS May 23, 1950' Filed Oct. 29. 1948 FIG? l.. 1'. ANDERSON ET AL l 2,509,050

TIMED TRUNK RELEASE 3 Sheets-Sheet 2 I IAA/@msnm /fvl/E/vroRs MC GODDARD ATTORNEY May 23, 1950 T. ANDERSON ET Al. 2,509,050

TIMED TRUNK RELEASE Filed oct. 29, 1948 s sheets-sheet s E//VG/NG SUPPLY CODE CODE GEN @ING/N6 GRD,

L7.' ANDERSON /NVE/VTORS M C GOUDA/70 By @am A TTOR/VEY Patented May 23, 1950 UNITED STATES PATENT OFFICE TIMED TRUNK RELEASE Lynn T. Anderson, East Orange, N. J., and Myron C. Goddard, Garden City, N. Y., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 29, 1948, Serial No. 57,387

4 Claims.

invention is directed are particularly applicableV to a telephone system of the so-called cross bar type disclosed in the application of A. J. Busch Ser. Nol 57,394 led concurrently herewith.

In a, system of this type a marker is employed to control the operation of cross bar switches located on a line link frame and on a trunk link frame to select an idle channel extending from a desired subscribers line to one end of an idle intraoce trunk circuit which terminates at both of its ends at cross-pointsI of cross bar switches on the trunk link frame. This selected channel is set up in accordance with the digits of the desired line number dialed by the calling subscriber. When such channel is selected and the marker nds the desired line to be idle, Vthe marker then selects an idle channel extending from the calling line to the other end of the intraoflice trunk circuit and operates cross bar switches on the line link frame on which the calling line terminates and on the trunk link frame on which the selected intraoiiice trunk circuit terminates in accordance with the selected channel to interconnect the calling and called lines.

The intraoiiice trunk circuit in accordance with the present inventionprovides the necessary equipment for supplying ringing current to the called line as selected by a ringing selection switch and applied to the trunk circuit under the control of the marker; for tripping the ringing upon the response of the called subscriber; for furnishing transmitter battery supply to both the calling and called lines and for providing supervision on the established connection.

It is an object of the present invention to provide an intraoiiice trunk .circuit of the character above-outlined which shall be simple in structure and reliable in operation.

The novel features of the invention by which this object is attained are setforth in the appended claims and the invention as to its organization and its mode of operation will be best un-` derstood from the lfollowing detailed description when read in Aconnection with the drawing in which: Y

- Fig. 1 shows schematically the vequipment ot an oice of the crossbar type by which a calling lineA` and a desired or called'line may 'be connected to .tending from the registers to the marker, the

the incoming and outgoing ends of an intraoilice trunk circuit;

Fig. 2 shows an intraoiiice trunk circuit embodying the present invention; and

Fig. 3 shows a ringing selection switching ciri cuit selectively operable to select the type ofringing required for any particular connection over the intraoice trunk circuitand for connectingl the selected ringing current source to the trunk circuit.

For a complete disclosure of the invention, Fig. 2 should be placed to the right of Fig. 1 and Fig. 3 should be placed to the right of Fig. 2.

. The switches .schematically disclosed in the boxes of Fig. 1 labeled Line Link Frame. and Trunk Link Frame and the ringing selection switch of Fig. 3 are of the well-known cross bar type such as is disclosed for example in Patent 2,021,329 granted November 19, 1935 to J. N. Reynolds. In the switch of Fig. 3, the select magnets are selectively operablefrom the marker in accordance with the setting of the number group to.

divdualized to ten trunk circuits, one of which is shown in Fig. 2, to which the ringing selection switching circuit of Fig. 3 is common. f

The circuits and apparatus schematically disclosed in Fig. 1 of the drawing are fully disclosed and described in the application of A. J. Busch hereinbefore referred to and such portions of said application as are of assistance in the comprehension of the present invention are to be considered as embodied in the disclosure of this application. q

The invention will now be considered in detail. It will be assumed that the calling subscriber at the substation designated |00 in Fig. l, initiates a call whereupon'a connection is established from the line link frame |06 on which the calling line y terminates to an idle marker |50. Access to the to select an idle originating register, such as is schematically disclosed by the box |02, which will later serve to transmit a dial tone to the calling line and to receive dial pulses.

vOriginating registers are distributed over the trunk link frames.- Bymeans of test leads ex- 3 marker determines which trunk link frames have idle registers and which frames are not being used by other markers. It then preferentially selects an idle frame with idle registers and connects to the frame through the trunk link connector. The marker then preferentially selects an idle register and connects to it. It will be assumed that the; originating register |i|2L is idle and is accessible`V from the idle trunk link frame |93, which frame is connected to the marker through the trunk link frame connector |04.

The determination of the location of the (falling line is begun as soon as the marker is seized andY continues while the marker isf selectingY an` idle register. Line location is made in terms ofY the line link frame, the vertical group, the horizontalv group and the vertical file. A line link vertical-j group of subscribers lines is five verticals wide and ten switches high. Following marker seizure,y

the marker determines which vertical group contains the line awaiting service. Thevertical:groupl contains a maximum of fifty subscribers lines, therefore the determina-tion of the vertical group localizes the subscribers linesl as within fifty of the maximum of 690 lines terminating on the frame. Y

A line' link horizontalgrou-p of subscribers lines. isA one switch high and the width: of thel supplied line of switches, the maximum Width being that oi a frame containing fourteen ver# tical groups; Theinfarker determines which horizontal group has; one or more lines Within the selected vertical, grou-p. awaiting service and. the marker then, preferentially selects oneY group. TheV line' to bei served hasnow been located withiny ve lines. as determinedA by the selected vertical and. horizontal groups.

Line location does not proceed past the-hori-v zontal group selection. until the marker has seized. the trunk linkframe. Following trunkV link frame seizure, the marker seizes the. line linktA frame |051whi'ch has.identiiiedv itself through. its marker connector inl'y whereby leads are extended to the. markerv for vertical le identication and Afor corn-pletingA connection to` the frame. A line lin-kl vertical ille. of subscribers?" lines is one verticatwide' and ten switcheshigh.A Thus one vertical group contains live vertical illes.V The. marker tests the' iivelines found inL thev vertical le in which. the calling line is 1o-A c'ated and if more than one line arev awaiting service; the marker preferentially selectsA one.- Tl'iel marker `their transmits the line link framenu'rnberand the selected linelocation tothe originating register.

After the horizontal group has been determined and an originating register seized, the marker selects one of ten channels which may` be usedto connect the calling` line to the reg' ister. The marker tests the junctor, lirielink and trunk link in each channelto see what junctors or linksare already' in use on other calls.V Thelowest numbered available channel is chosen andthe markerH operates the select and holclly magnets on the lineV linkand trunk-link frames to establish the channel. It has been assumed that the selected channel extends over the linelink trarne H36 and the trunk link frame |53. When the channel is selected,- the marker indicates to the register the number of the line ister the line link` frame number, calling line:

4 location and the line link number used in the dialing connection to the register |32.

The calling subscriber then receives a dialing tone from the selected originating register |02 after which the subscriber proceeds to dial 'the digits of the wanted line number, which digit impulses are registeredin the originating registere.A After-the entire number hasv been dialed, the register calls in a marker over the originating register marker connector |91. As soon as a marker has been connected to the register, the register proceeds to transmit to the marker the calling subscribers line link frame location which is-`V` then registered in the calling line number register |5|V` of the marker, the office code digits of the called' line number which are registered in the'V calledfoitice-code register |52 of the marker and thev numerical digits of the called line number which are registered in the called line number register |53 of the marker. From the called office 'cede register |152, the marker proceeds through thetran'siatorf circuit i5( to deter-mine the "outing of? the desired connection tlierelc'iy rein the operation ofareute relay in'fthe glfoup ei route` relays |55'. Itf will be e'lss'uril'edv that in the cals'el under consideration theI desired subscribers' line |f08l terminates thesame office asVv the calling line H10 and'- that= therefore' the selected route/'- relay isVV effective to` control'- theY setting up of a connection between the subs cribersv lines over arr intraoftce trunk:

Toy accomplish this;l the? marker' seizes-- an idle trunkiink frame whichhas idle intraomcetrunks; It willL be assumed that the trunk link fratrien HU: is seizedV over the trunk link connector |59z and connects to anidle intraomce trunk, for examplev the-trunk shown in Fig. 2f.

Wiiue trunkseleicticn'i's' taking place', the mark-- er determines thel line link framje location ofthel called linebyconsulting thenumber group. The marker seizesY the ru'mloer group' fratrie' IIA2 over the' number' group' Connector II and passes the riurrerical4 digits ofthe called number'to it from' the called line number register` |53. The num-` ber grrn'n'q translates the r'iumerical'` digits into the location inrt'erms; of line link frame number,y vertical groupr hdri'zontalf groupand vertical file. The number group also'gi'ves the marker infor,- mation for setting the. ringingY selection switch` for ringing the called subscriber. The intraevince trunkl circuits appear onY a vertical file of thegswitcn and differentv ringing codes appear on` thehorizontals, Themarker after receiving'the required-informationfromA the number vgroup and after an' idle channelI has been selected, operates the selected hold magnet tot connect'r theA proper individual or` party line; ringing into the` trunkcircuit;V The marker` then disconnects and1 leaves the' switch heldf by the trunk circuit.

The marker seizes the line'linkgframefon which theA desiredflineterininates.after the called number infoi'inati'or has-,been received from the numf` ber groupzand'afterfthe trunlclink frame has been.

seized. It will be assumed; that tlieline link` frame |1| 4 is. seizedf tliroiliglr` theline link connector |l| 5. The. calledI lin'ef Wilnis' thenv selectedandtested for-its idler or busy condition. If the called line .isA idle, the. marker intercormeetsy the calledline and' thev-intraoince trunk circuit by-ai'r idle channel.- The marker'testsftoiseewhatijuncQ-r tors are already in use on other calls. The lowest numbered; available channel is chosenandthe markeroperates the select adlholdinagnets onCA to establish theV channel. If the called line is busy, the calling line is connected through a. channel to a tone trunk terminating on a trunk linkarame in the manner set forth in application Serial No. 57,382 of J. Michal filed October 29, 1948. y

After the marker establishes the terminating connection, it seizes the line link frame |06 of the calling subscriber and selects an idle channel between the intraoce trunk andthe calling line. The dialing connection previously established is not released until the marker determines that an idle channel exists between the calling line and intraoffice trunk.

The marker has recorded the number of the line link used in establishing the dialing connection to the originating register |02 and may therefore reuse that line link as part of the originating connection-if thelink is part of the lowest num- 4bered available channel. rBhe marker then proceeds to operate the select and hold magnets on.

the line link and trunk link frames |06 and ||0 to establish a co-nnection from the calling line to the intraoce trunk over the selected channel. The calling subscribers line |00 is now connected over the line link frame |06, the trunk linkI frame I0, the intraoffice trunk and the line link frame ||4 to the called line |03. The marker now becomes disconnected and releases the originating register |02. Y

It has been assumed that the marker |50 has through the trunk link connector |09 been directed to the trunk link frame H0 on which an idle one of a group of intraofce trunk circuits terminate. The ends of each trunk circuit, termed the A and B appearances, terminate in the same level of different switches of the trunk link frame.

There is a frame test (FT) lead 200 for each trunk link frame on which intraoflce trunk circuits appear and each idle trunk circuit supplies ground from the upper back contact of the SI relay to such test lead. The marker has access to the test leads, such as 200, through the trunk link connector |09 and knows that there is at least one idle trunk circuit on each frame corresponding to a grounded lead 200. The marker then proceeds to select one of the frames with available trunk circuits .and supplies ground on the frame (F) lead `202 to all the intraoiiice trunk circuits appearing on that frame. It will be 4assumed that the trunk circuit shown in Fig. 2

- mining the cross-point in a horizontal level of ais one of such trunk circuits which appear on the trunk link frame ||0. This ground on lead 202 is applied over the lower normal contacts of the make busy (MB) switch 203, over the lower back contact of the S| relay 20| to the right terminal of the winding of the F relay 204 of each trunk circuit that is idle. The marker determines which of the trunk circuits are idle while looking for this ground through the windings oi the F relays and over the busy (BT) rlead 205 selects one of the idle trunk circuits. These trunk link frame and trunk circuit selections are carried out by the marker in the same general manner as the originating register selection previously referred locks out vall other markers from such frame until the marker |50 has completed setting upthe connection.

" Relay 204 upon operating connects ground over 1- its lower No. 2 contacts to the FA lead 206 extending to the trunk link connector |09 for deterswitch on the trunk link frame ||0 where the B appearance of the trunk circuit is located and connects ground over the upper back contact of the CS relay 201, lover the lower No. 3 back con-l tact of the CH relay 208 and the lower No. 3 contacts of relay v20-| to the FA lead 209 extending to the trunk link connector |09 for determining the cross-point in a' horizontal level of a switch on the trunk link frame l0 where the A appearance of the trunk circuit is located. This latter ground connection is established over back contacts of relays 201 and 208 to insure that such relays are unoperated and their contacts closed before the marker sets up a connection on the trunk circuit to guard against a timed release as will be discussed later. to the FA leads 206 and 209 causes the operation of FA and FB relays (not shown) in the trunk link connector |09 which in turn cause the operation of a level LV relay (not shown). tion of the FA and FB relays perform the necessary functions in conjunction with the marker to set up the connection between the calling subscribers line |00 and the called subscribers line |00.

One of these functions is the transference of the sleeve leads 2|0 and 2|| to the marker |50 for testing and the tips and rings from the trunk circuit to they marker for continuity checks to the subscribers lines. In addition the operation of the LV relay of the trunk link connector establishes la circuit from the marker to the SI lead 2| 2 of the trunk circuit, thence over the upper No. 1 contacts of F relay 204 and through the winding of the Sl relay 20| to battery and ground so that the marker causes relay 20| to operate.

Relay 20| upon operating makes the trunk circuit busy by opening the F lead 202 at its lower No. 5 back contact, thereby opening the initial operating circuit for the F relay 204 and at its' upper No. 1 back contact removes ground from the FT lead 200 so that if all the intraoftice trunk circuits on the trunk link frame H0 become busy,4

the FT lead 200 will not be grounded and the trunk link frame will test busy to any marker. Relay 20| also connects ground through the l0- ohm resistor 2|3 over its upper No. 3 contacts to sleeve conductor 2|0 of the A appearance of thel trunk circuit and connects ground over its upper'i No. l2 contacts and through the 10-ohm resistorv 2`|4 to sleeve conductor 2li of the B appearance of the trunk circuit to provide holding grounds;

trolling the delayed priming of the CH tube'2l18 but this is not effective until the CS relay 20'| operates upon the response -of the called subscriber, since the condenser 2|`| is shunted by4 ground applied over the upper back contact of relay 20`|V and the lower back contact of relay 208.

In the meantime, the marker has received information from the number group frame I 2 concerning the type of ringing to be supplied and has .operated select magnets of the ringing selection The connection of ground The operacross bar switch, of Eiga-allocatedtothetrunk circuitsappearing on the. samef'level of .each-.ofv the ten trunk switches on the trunk link. trame; 110i. It will be assumed that for ringing; the

called. subscriber 10.8, the marker completesthe. 5,;

circuit through. ther trunk link connectorY maand through the winding of; select magnet. 3.0.6 toi ground .to enable the. application of negativesuperimposed ringing. for. .two secondsV followed; by alom-second .silent interval and themarker also. establishes acirouitv for the select. magnet. 300 so that. the. above ringing is applied to the ringf conductor and ringing ground to theAv tip conductor, A-f-ter the; select magnets. haverheen operated; the marker connects around to the RC lead 219 therebycompleting aclrcuit from .groundon Such lead, over .the upper No. 2 contacts ofthe F-relay 204 and through.. the winding of the. ringing; control RC relay 2.20 toVv battery andground. v

Relay 22u thereupon-.operates and establishesa. circuit from ground over the lower'No..v 2 contacts. of the SIl relay 2.0.1.,.over they lower No.. 4- back contact. of the CH relay 208,A over the lower` No. 3 contacts of relay zzcandconductor: 221 through the winding-of hold 'magnet 31.0 of the. ringing selection switch which magnet is individual tothe intraolce trunk circuit of Eig.. 2. this connection it is to be notedthat the other nine holdr magnetsof. theswitcnmay be allocated tov other. intraofllce trunk .circuitsto 4revertiye rings ing trunk circuits or to incoming trunk circuitsv whichhave appearances on thesame trunk link frame H0; The operation. of hold, magnet 31.0.: with the select magnetll operated as previously described,v establishes a locking circuit for. the:

Y for the. RC relay 22B., .at its lower No. 5 .back 4contact prepares the A.circuit for firingthe `tulle 2.1 Saafter the called subscriber has answered., .connects the pick-.up supply over its upper No. 3 hackcontaet, the lower No.` 5..contacts0.f the RG relay 2.20, the upper normal contacts of picks-up (PUlrelay 225. to the pick-up lead 22B-extending to the ringing selection switching circuit offF'ig. 3 and at `its lower No. 2 and. No. 3contacts disconnects ground from thetwo FA leads ,2.06 .and 209 thereby releasing the FA and FB vrelays (not shown) in the trunklink. connector :circuit 109.

The release of these latter relays .causes theV calling and called.. subscribers lines L00 .and 1.08` to 'be connected through to .the intraoilce trunk circuit.

With the calling line connected to the'intrahold relay'20'loperated after itsin-ital operatf y circuit hasheen openedA upon the release4 of 75 the lower No. 2 contacts of' relay 20|.

ther-relay 2114-. Reny 2m; lesion 1x1-.releasing and'. will. hold' overY this. interi/alf.A it; should beA notedy that. had; the; `call been abandoned' w..l1i1ev the. marker wasl function ipa the S .relay 2.21

wouldfnot. operate toestablisli the holiiinacrcuit for relay 20| and consequently relay 20|A would release followimg the. release ciY their relayv 204 restoringv theA` trunk `circuit tofnormal.

When the call for a one ring station. as

willy be. assumed.. the. .PU- relay.A 2.2.5-

immediately operated without. awaiting.v the. clos/lire of the interruptor contactsat tnepicknup supple* conneetedoyer the. .upper No .back contact .oi relay 204, relay 225 in this instance; being`r oper- Jr ated over a circuit extending from; battery through the winding of pick-up relayz, over the upper No. 1 back Contact of the. CH relay 208, over the'lower No. 4 contacts of Athe RC relay 220, thePKU lead 226, the left cross-point. contacts closed through the. conjoint operation of select magnet 306 and' hold magnet 310 and. the left cross-point contacts closed through the;

conjoint operation of select magnet 300 and hold magnet SM05 conductor 224 andv to. ground over Relay 225v upon operating locks in a circuitouer the upper No. 1 back contact of relay 208', over the lowery No. 4 contacts of relay 220, the upper alternate contacts of relay 225 and to ground over the 3i) lower No. 2 contacts of relay 20|.

`Ringingeurrent is now connected to the called line `from the ringing current supply 3H, over the outer right cross-point contacts closed through the conjoint operation of select magnet 306 and hold magnet 3I0, over the RT lead 312,

throughthewinding of ring trip (RT) relay 222', over the RB lead 313, over the next-to-Quter right contacts of the cross-point contacts closed through the conjoint operation of select magnet m 300 and hold magnet 3h0; over the ring (R) condoctor 3M, over' the lower contacts of pick-up relay' v225, over .the `lower No.. .2. iront contact of relay V22.0, over the ring. .conductor B of the trunl;

circuit, over .the ring of the established-connection to the .called line, `returning over the' tip of the established connection, .the tip (T) conductor of the B appearance of the .trunk oirouit,.ov,er .they

upper No. 2 yfront .Contact .of relay 22.0., over the upper innerl .contacts of relay 225, tip (T) lead 3.4 the next-.to-inner` contacts .oi `the .crosspoint 4contacts closed through .the conjoint operel ation of select magnet 3.00 .and holdf'magnet 3l0 and tothe ringing ground at the ringing .Cllr-rent supply 311;. At the sometime rinsing teneis Supplied to the .calling line .through oondensere Zita-nunc.' and .over the connectionestablished over .the A appearance of vthe trunkxoircuit to the calling subscriberis line 1.00.

itfithe Acall -is not' fora "one ring station, the pick-up relay 225 Adoes notreceive.aV direct .opere ati-n'gground-over the cross-points .of the ringing selection switch as just described but awaits a groundccnnection over the -upper No. 3 back .cone

omas trunk circuit.) over the A appearance ofthe 65..- tact .oithe F relay 2041to'insure that 'machine forth-inthe copending application oM. G. Goddardu Serial No. I573386, filed October 29, 1948.

Should the call lloe'abandoned before the called subscriber' answers, theY S-r'elay 2,21 releases -inv turn'A releasingf'the Sl'relay 201l^which Areleases ingtheY oiiice may be accomplished lasiully set- 9 the connection and restores the trunk circuit and -associated ringing selection switch vertical to normal.

When the called subscriber answers, the increased current ow from the ringing or silent period voltage operates the ringing trip (RT) relay 222 thereby causing the release of the RC relay 220. Relay 220 upon releasing opens the circuit over which ringing current was applied to the called line and the circuit over which ringing tone was applied to the calling line and the RT relay 222 releases. With relay 220 released, the upper winding of the CS relay 201 is connected over the upper No. 3 back contact of relay 220 to the tip conductor of the connection established to the called line |08 and the lower winding of relay 201 is connected over the lower No. 2 back contact of relay 220 to the ring conductor of the established connection whereupon relay 201 operates. Relay 220 also at its lower No. 4 contacts opens the locking circuit of the PU relay 225 which releases and at its lower No. 3 contacts opens the circuit of holding magnet 3|0 of the ringing selection switch therebyv releasing the vertical of such switch used in conjunction with the trunk circuit of Fig. 2.

The supervisory relays 221 and 201 have carefully balanced windings and the tip and ring condensers 230 and 23| in the talking circuit of the trunk circuit are closely balanced in capacity to provide a good talking circuit.

The CS relay 201 upon oper-ating removes ground at its upper back contact which keeps condenser 2|1 discharged. This condenser now charges toward the `|130volt potential applied through resistors 2 I 5 and 2 6. The time constant of this charging path is such that it takes from two to ve seconds for the voltage across condenser 2 l1 to reach the value that will cause the CH tube 2|8 to break down on its control gap. If the CS relay 201 should release before the tube breaks down, the condenser 2| 1 is rapidly discharged through resistor ZIB. When tube 2|8 does break down on its control gap, the main gap then conducts and establishes a circuit across such main gap through the upper winding of the CH relay 208, over the lower No. vi back contact of the F relay 204, over the lower No. 1 normal contacts of relay 208 and lto ground over the lower No. 1 contacts of the SI relay 20|, to ground over the upper contacts of the S relay 221 or to ground over the lower contacts of the CS relay 201. Relay 208 upon operating locks through its lower winding and lower No. l alternate contacts to ground as traced at contacts of relays 221 and 201. When relay 208 opens its lower No. 1 transfer contacts, it opens the circuit through tube 2|8 thereby extinguishing the tube to obtain long life from the tube. The CH relay 208 is locked until all three relays 20|, 221 and 201 have released at the end of the call and supplies an additional ground over its upper No. 3 contacts, the upper No. 3 back contact of the RC relay 220 and through resistor 2li! to` l circuit from battery through the winding of the RC relay 220, over the upper No. 2 contacts of relay 208, contacts of heater unit 232, over the' lower No. 3 front contact of relay 208 and to ground at the upper back contact of relay 201. Relay 220 thereupon operates and opens one holding circuit for the S| relay 20| at its lower No. 1 back contact and with the other holding circuit of relay 20| opened at the lower No. 2 back contact of relay 208, relay 20| now releases removing ground from the sleeve conductors 2|0 and 2 I at the ends of the trunk circuit thus releasing both the calling and called lines and restoring the trunk circuit to normal through the release of the S relay 221, followed by the release of relays 208 and 220 and the restoration of the heater unit 232. The reoperation of the RC relay 220' was ineffective at this time to reoperate the PU relay 225 since the circuit of relay 225 was opened at the upper No. 1 back contact of the CH relay 208. Also relay 220 was ineifective to operate the hold magnet 3|0 of the ringing selection switch since the circuit for such magnet was opened at the lower No. 4 back contact of the CH relay 20B. The timed release of the connection if the called subscriber disconnects rst as just described, prevents a calling subscriber from holding a called line out of servvice indefinitely should the calling subscriber fail to disconnect following a disconnection by the called subscriber.

When the calling subscriber disconnects first, the release of the S relay 221 opens at its lower contacts the circuit of the SI relay 20| and Such relay releases and disconnects resistance ground at its upper No. 3 contacts from sleeve conductor 2|0 of the connection toward the calling line and by closing its upper No. 1 and` lower No. 5 contacts indicates that the trunk circuit is again idle. The CH relay 208 is still held operated b y the locking ground applied over the lower contacts of the CS relay 201 and consequently ground is connected over'the upper No. 3 contacts of relay 208 and the upper No. 3 back contact of the RC relay 220 through resistor 2M to sleeve conductor 2|| to hold the trunk circuit connected to the called line.

This reduces the possibility of a false start of an origin-ating register and the unnecessary use of the marker. Under this condition a circuit is established from ground over the lower No.v 2 front contact of the CH relay 208, over the lower No. 3 back contact of the SI relay 20| and through the winding of the heater unit 232 to battery. After a fifteen-second interval the heater unit closes the circuit of the RC relay 220 which now opens the circuit of the CS relay 201 and removes ground from the sleeve conductor 2| to release the connection toward the called line. Relay 201 upon releasing also opens the locking circuit of the CH relay 208 which then releases permitting the heater unit 232 to restore and releasing the RC relay 220. If the called subscriber disconnects before the RC relay 220 operates, the CS relay 201 releases releasing the CI-I relay 208 which then removes ground from the sleeve conductor 2|| releasing the connection toward the called line and restoring the trunk circuit to normal.

lf the trunk circuit is reselected by a marker while being held -by the called subscriber, the marker causesthe operation of the F relay 2,04

vwhich connects `ground tothe FA lead `205 in the B appearance toward the called line. This operates the FA relay (not shown) in the trunk f Vloeen .made lousy.

asoman `link `connector l-iltl which opens '.tloe tip `ring .and .sleeve `.conductors *of 'the appearance tthusreleasing theCS relay ,2li 1 and .in fturn releasing ther-1H .relay 29B. The trelease of :relay .1288 removes Agroundirom thefsleeveconductor 2M thuslfreeing :g

the .trunk circuit from `'the called :l-rne so that the f new call vcan Aloe completed :by the Amar-ker `without.

.urtherinterference Thelma-ke vlousy MB switch 203 is used .to rmake .the :trunk circuit husyat any time. .Itimay beV seperated Without `interaerineT with any call that .may `be intl-1e trunk circuit fbecause it merely opensltlce ET-.andlleads -Zlilband 2102 whichfare l.already-open if zthe trunk-circuitfisfin use. -When the .trunk circuit -is made busy and ris '-not Yinluse, :the .ground .normally supplied fto the FT;lead 2-3!! .is applied to the MBL lead 2733 fto light a lamp ,common tto .the -trunk circuits .on the trunk ylink .frame :4l-El :as an .indication that rthereise .trunk ,on that iframe which .has #been-made busy. .'-lhe switch 203 also transfers -.the fcircuit :for fopera-t- ,ing lthe F relay .294 .from -the .-F lead i292 to Lthe TF lead 234 .whereby .tlievlmarker `can .route test -call to a particular itrunk .although .-it has @n such .a lcall :the marker will connect -ground not only to lead *282 but fto .lead 234.

The 1.0-ohm ground .is supplied lto eachoffthe .sleeve conductors 24!! and 2M to hold .the hold magnets `so that xa particular trunk .circuit .may be marked, even when busy. with .a slight {eosi- J.ti-ve potential. This .potential :indication .is used on .calls such as -no testcalls.

The release .of theswitches lon .the line .link

-and trunk .link -tramesover vwhich the-connection ,has -beenfestabl-ished accomplished -in .the yWell- .known lmanner .and a description thereof herein zisideemed to beunnecessary.

What .is claimed Iis:

1. 1n altelephonelsystem, acallinglineua called .-line, fa trunk circuit. common .control means for -fcontrollingr the establishment of 'a connection loe- .tween said lines including fsaid trunk lcircuit, a .source I-of 'rinsing current, a .-relay .said Vtrunk circuit .controlled from fsaid common control `mea-ns :to connect'said source of 1f-inning current with said trunk circuitto said called line, means operative .upon .the lresponse ofthe called isubscriber to cause the release of .said .relay to 1disconrueot lsaid .source of ,ringing .current trom Vv'said trunk circuit, .timiner .means in .said .tmnk circuit lmeans responsive to .the release .of .said

`connection .fat either end of said trunk .circuit to initiate the of said .tirnifne .mea-ns,

.a circuit controlled. .bysaid timing-means for re- ,f operatinc .said relay, :and -means controlled .by `said relay @upon .its .reoperation .to release the otherend-ofsaid connection.

.2. .In va .telephone system..a .calling line, .acalled vline, a .trunk circuit, .common .control means for `controlling .the establishment .of a Aconnection .between 4said .lines including said .trunk circuit, a .source of ringing current, aringing control Arelay in said trunk .circuitlcontrolled frornsaid `common control means preparatory A.to .connecting said .ringing currentsource with .said .trunkcircuit, a ,pick-up relay .responsive tothe operation of said latter relay for completing 4the connection of said source of rinsing ,current with said trunk circuit, a .relay operative upon the v.response oi the called subscriber to cause the vrelease of said ringing control relay to disconnect said suurce of ringing current from said trunk circuit, timing means 'in .said trunk circuit, means kresponsive 'to the 12 release lof .said .connection at .either .end `of said .trunkcircuit to .initiate.the-operation.of-said ltiming means, a circuit controlled by said .timing means for .reoperatingsaid ringing Acontrol-relay, .means Acontrolled loy .said .latter .relay upon yits .reoperation to ,release the l.other end ofsaid nonnection, and a. .relay operated ollowing the disassociation Yo f said common .control means from lsaid -trunk circuit for preventing .the reoperation of 'said pick-up relay upon the reoperation of said ringing "controlrelay,

3. In atelephonesystem, va callingline, Aa called line, `a Vtrunk circuit, common control means for controlling fthe establishment of a connection between said lines including said trunk circuit, a'plurality of sourcesof ringing current, asuf'itch 'forselecting'any one of said'sources controllable by saidcommon control means, a relay in said 'trunk circuit controlled from said common control vmeans to connect said selected source oi ringl"ing Icurrent with 'said 'trunk circuit 'to signal said tcalled subscriber, 'means operative uponthe response 'of fthefcalled'subscriber to cause the release -of 'saidrelay to disconnect said selected 'source of ringing #current-'from 'said y'trunk circuit, Itiming means fin 'saidtrunk fcircuitfmeans 'responsive `to the release 'of said conn'ectionat leither 'end 'of .said trunk circuit to 'initiate the operation 'of said timingmeans, 'a lcir-cuitfcontrollecl l*by said timing means for y.reopera'ting said irelay, and means controlled -by said :relay `.upon .its reoperation -to release the other end-ofsaidsconnection 4. In artelephone system, arcalling line, a called line, a trunk-circuit, 'common :control means .for :controlling tlievestablishment .fof a connection -between said Ylines .including said trunk circuit, -alcrossbarswitcli comprising a plurality of lcrosspoint .contact fsets, -a `plurality of sources of ring .ing current associated .with-.said contact sets, .means -under the :control .of said common control .means to .prepare a plurality :of .said contact-sets Ato select .one of `said sources vof ringing current, a relay lin .said trunk` circuit .controlled .from said common .control means .to .close said prepared contact ,sets and to connect saidselectedr-inging `current source with said ltrunk circuit `to signal ,said called .,line, .means operative upon .the response of the called subscriber to cause the release .of said .relay and .said switch lto disconnect .said selected source of ringing current from said trunk circuit,`timing.means in said 'trunk circuit, means responsiveV to the release of said connection at 'either end of said trunk circuit to initiate .the operation of Ysaid timing rmeans, a vcircuit con- *trolled by said timing means for reoperating said relay, .and means controlled by said relay upon 'its `reoperation:to release l the other end of said connection.

LYNN iT. ANDERSON. MYRON C. GODDARD.

REFERENCES CITED The following references .are of record in the iile of this patent:

.STATES PATJH NTS Number Name Date 2,031,692 Carson Feb. 25,1936 23965;894 Hovland Dec. 29, 1936 254303316 Voss Nov. 4,1947

FOREIGN PATENTS n .Number lCountry Date .779,939 France Jan. 24, .1935 

